In recent days, there is a structure which has an obstacle detecting apparatus and an alarm in a vehicle traveling on a highway or the like, detects an obstacle existing on a traveling road by an obstacle detecting apparatus and informs an operator of an existence of the obstacle by the alarm. Further, in an unmanned dump truck which travels on a fixed course in a mine or the like, it is structured such as to detect the obstacle existing on the course by the obstacle detecting apparatus and automatically control the vehicle by a brake.
The obstacle detecting apparatus is roughly classified into a transmitting and receiving type and a receiving type, and both commonly have an ultrasonic type, an optical type, an electric wave type and the like. In this case, an ultrasonic type and an infrared light type are preferable for detecting a short distance (shorter than about 15 m), a laser light type is used for detecting both of a short distance and a long distance, and a millimeter wave is preferable for detecting a medium distance (about 120 to 150 m at the shortest). The details are as follows.
The transmitting and receiving type has an outgoing device for outgoing a medium such as a sound, a light, an electric wave and the like in a traveling direction of a vehicle, an incoming device for incoming a medium reflected by an obstacle existing in an outgoing direction of the medium, and a calculating device which receives the outgoing medium from the outgoing device and the incoming medium in the incoming device and calculates a distance from the vehicle to the obstacle on the basis of a difference between them so as to define an existence of the obstacle on the basis of the distance. In this case, the "difference between them" means a time difference between an outgoing time of the outgoing medium and an incoming time of the incoming medium, and in the case of the millimeter wave or the like, in the calculating device which employs a frequency analyzing process such as an FM-CW or the like, it means a strength difference, a phase difference or the like of the incoming millimeter wave.
The receiving type is structured such that the outgoing device is omitted in the transmitting and receiving type mentioned above, and corresponds to a receiving side in a so-called beacon, however, in a structure for a vehicle, since the transmitting device can not be provided in all of many and unspecified obstacles (stones, rocks, cliffs, animals and the like) existing on a traveling road, in most cases, an image processing type is employed.
In this case, the obstacle detecting apparatus is connected to an alarm and a brake so as to constitute a safety mechanism, however, when a trouble is generated in the obstacle detecting apparatus itself, a requirement for a safety can not be satisfied. Then, for example, the following monitoring mechanism for the obstacle detecting apparatus is disclosed.
(1) Japanese Patent Unexamined Publication No. 6-88870 discloses a technique which monitors a gate current of a transistor installed in an obstacle detecting apparatus and judges "an abnormality" when the gate current is out of a standard.
(2) Japanese Patent Unexamined Publication Nos. 57-42866 and 5-157850 disclose a technique which pays attention to a fine reflected sound inherently unnecessary and yet detected out of a course generated due to a non-directivity of a radiant sound, in the ultrasonic type and judges "an abnormality" when not detecting it.
However, the prior art mentioned above has the following problems.
(1) In Japanese Patent Unexamined Publication No. 6-88870, it is definitely judged that "an abnormality of the transistor is an abnormality of the obstacle detecting apparatus", however, there is a problem that it is not definitely judged that "an abnormality of the obstacle detecting apparatus is an abnormality of the transistor". For example, when a dust and a mud are attached to a surface of the outgoing device and the incoming device, a strength of the outgoing medium and the incoming medium is reduced, so that at this time, it should be judged that "the obstacle detecting apparatus is abnormal", however, it can not be always said at this time that "the gate current of the transistor is out of the standard".
(2) Japanese Patent Unexamined Publication Nos. 57-42866 and 5-157850 relates to a monitoring technology with respect to the ultrasonic type having a non-directivity, however, it is hard to apply the monitoring technology to a laser beam having a strong directivity, a millimeter wave which can freely set a directivity and the like. Further, since the laser beam and the millimeter wave are structured such that a detecting accuracy is largely changed in accordance with a dust in an air, a size and a shape of the reflected object, a ground clutter and the like, it is hard to detect a fine reflected medium and to set a judging standard with respect thereto.